Radioactive iodine treatment has been widely used for nearly 50 years in the treatment of thyroid cancer to ablate residual thyroid tissue after thyroidectomy and to treat metastatic disease. Leukemia is a rare complication associated with the radioactive iodine therapy. The occurrence of leukemia is known to be related to the cumulative dosage of I-131 more than 37 GBq (1 Ci) and also associated with the intervals of less than 12 months between the repeated doses. We report a case of a 52 year-old female patient with papillary cancer of thyroid who developed acute myelogenous leukemia after the total 20.4 GBq (550 mCi) of I-131 therapy over 3.2 years and palliative radiation therapy (3000 cGy) due to multiple bone metastasis of papillary cancer.